Method of producing stable polyurethane solutions

ABSTRACT

A method for improving the solution stability and homogeneity of substantially linear polyurethanes obtained by the reaction in solution of a diamine chain extending agent with an isocyanateterminated prepolymer.

United States Patent Ikeda et al. 1March 20, 1973 METHOD OF PRODUCINGSTABLE [56] References Cited POLYURETHANE SOLUTIONS V UNITED STATESPATENTS [75] Inventors: Yuichi Ikeda, Yokohama; Choji Yuyama, Kosakai;Tsuguhisa Hiru- 3,378,511 4/1968 Newton ..260/77.5 AP kawa, Kosakai;Yoshio Isshiki, 3,475,266 10/1969 Strassel 260/775 AM Kosakai, all of Japan I T Primary Examiner-Donald E. Czaja [73] Asslgnee. Anehotex,lnc.,New York,N.Y. Assistant Examiner M. J. welsh Flled! p 3,1971 Attorney-James E. Ryder et al. [21] Appl.No.: 177,632

[57] ABSTRACT 52 US. Cl "260 775 AA, A method for improving the solutionstability and 26 0/30l6 R, 2 60/30.8 D S, 260/326 N, homogeneity ofsubstantially linear polyurethanes ob- 260/77 5 AM tained by thereaction in solution of a diamine chain [51] Int Cl extending agent withan isocyanate-terminated g prepolymen [58] Field of Search..260/77.5 AM,30.8 DS, 32.6 N, 4 Claims, 1 Drawing Figure 260/306 R, 77.5 AA

METHOD OF PRODUCING STABLE POLYURETHANE SOLUTIONS BACKGROUND The usualprocess for producing a polyurethane solution is to first react ahydroxyl-terminated substantially linear polyester, polyether,polyacetal, polyester-ether, or the like with an excess amount oforganic diisocyanate to form an isocyanate-terminated prepolymer whichis then chain-extended in the presence of a solvent with diamines orother compounds containing two active hydrogens.

It is well-known that the reactions of an isocyanate group with activehydrogen compounds are exothermic and difficult to control and maintainuniformly in batch systems, particularly with fast-reacting systems suchas the conventional symmetric aromatic isocyanate-terminated urethaneprepolymers in combination with aliphatic, diprimary amine chainextenders. The result is that gel structures and other inhomogeneitiesare formed almost invariably during the solution chain-extension step,leading to rapidly increasing viscosity and eventually complete gelationwith the passage of time and to attendant difficulties in maintainingshaped article production and property uniformity.

Various methods have been proposed for reducing gel formation, such asdecreasing the chain-extension reaction rate by chain-extending at lowtemperatures, chain extending in two steps using two chain extenders ofdiffering reactivity, using stabilizers such as acetone during chainextension, or using a continuous chain-extension process in which onlysmall amounts of reactants are combined at any one time. Although theseand other prior art methods have been successful to varying extents, ithas still been difficult without basic and extensive modifications informulations and equipment, using conventional prepolymers and chainextenders, to produce a polyurethane solution industrially which isstable enough to be stored for more than a few days.

SUMMARY OF THE INVENTION This invention is a method performed in batchfor producing exceptionally stable and homogeneous substantially linearurethane polymer solutions suitable for production of films, coatings,filaments and other shaped articles. It also produces urethane polymerswith more uniform and more narrow molecular weight distributions thanthose produced by conventional methods.

The method is carried out by the reaction in batch in a polar solvent ofconventional prepolymers and diamine chain extenders at specified ratesof addition I of the reactants to the reaction zone within limitsexpressed by the following sets of equations in which Set ll expresses apreferred range:

Set II:DP+30% or, preferably added at any time, during the periodextending from the beginning to the completion of diamine addition,expressed as a mole percent of the total amount of each, respectively,to be added for completion of the reaction. As thus expressed, 65 to 95percent, preferably to percent, of the stoichiometrically requiredprepolymer solution should have been added to the reaction zone afterall of the diamine chain extender has been added.

In calculating the amount of prepolymer required at any given timeduring the reaction, all compounds containing active hydrogen atomswhich would react with isocyanate groups must be taken into account,whether monofunctional, bifunctional or polyfunctional, the degree offunctionality determining the corresponding amount of prepolymerrequired. Thus 1 mole of a monoamine chain terminator would be includedas a half-mole of a bifunctional chain extender for purposes ofcalculating the amount of required prepolymer according to the aboveequations.

DRAWING The FIGURE shows in graph form the equations set forth above.

DETAILED EMBODIMENTS AND EXAMPLES In carrying out the method of thisinvention, both solvent and a definite but small (hereinafter defined)amount of diamine chain extender may be placed in the reaction zoneinitially, followed by simultaneous addition of both prepolymer andchain extender at a rate falling within the limits established by theSet I equations above. The initial amount of diamine and rates ofaddition of the reactants should be such that all of the diamine chainextender will have been added when 65 to percent, preferably 70 to 90percent, of the stoichiometrically required prepolymer amount has beenadded. Once this point has been reached, the remainder of the prepolymermay be addedat any reasonable rate which will allow reaching the desiredsolution viscosity and still maintain a slight excess of amine groups inthe finished polymer. Alternatively, one may start with solventalone inthe reaction zone and add the chain extender ata greater speed than andsimultaneously with the urethane prepolymer, the rates of addition againconforming to the boundary conditions established by the Set I equationsabove. As above, all of the chain extender in this alternative case willhave been addedwhen 65 to 95 percent, preferably 70 to 90 percent, ofthe stoichiometrically required prepolymer amount has been added. Again,the remainder of prepolymer needed to reach the desired viscosity endpoint may then be added at any reasonable rate as in conventionalprocesses.

The above sets of equations are shown in graph form in the FIGURE, inwhich the limits of the Set I of equations are shown as I on the graphand the preferred limits of the equations of Set II as II. The equations(as more fully shown in the FIGURE) show that an excess amount ofdiamine chain extender should always exist in the reaction system. Inthis connection, the ratio of chain extender to prepolymer should be ashigh as possible in order to better control and keep the final polymerchain length from getting too high. It is desirable, therefore, to add 3to 30 percent of the total amount of diamine extender to be used to thesolvent in the reactor before adding the prepolymer simultaneously withthe remainder of the diamine. A more narrow molecular weightdistribution is obtained in this way. In line with this the chainterminator may be added towards the end of the chain-extension reaction,but it is preferable to mix it with the diamine chain extender and useit from the beginning of the reaction; this method also aids inobtaining a more narrow molecular weight distribution of the polymer insolution.

The uniqueness of this invention is the initial concentration of diaminechain extender used and the subsequent rates of addition of both chainextender and prepolymer with the limits set forth in the Set Iequations. By use of the method of this invention, usually homogeneousand stable urethane polymer solutions are obtained. If one works outsidethose limits of rates of addition of diamine chain extender andprepolymer, the resulting solutions obtained are stable for only a fewdays, less homogeneous in physical properties and more difficult tocontrol in viscosity and solid content from batch to batch.

The bifunctional urethane prepolymer having anisocyanate group at bothends of the molecule to be used Useful diamine chain extenders includehydrazines, ethylene diamine, propylenediamine, hex-- amethylenediamine,cyclohexylenediamine, methyliminobispropylamine, piperazine,2-methylpiperazine, naphthylenediamine, diaminodiph'enylmethane,phenylenediamine, toluylenediamine, xylylenediamine 3 ,3 '-dichloro-4,4-diaminodiphenylmethane, carbodihydrazide, carboxylic-acid-hydrazide,and mixtures of them.

The chain terminator useful in the method of this invention is acompound containing only one primary or secondary amino group, such asdimethylamine, diethylamine, dibutylamine, diethanolamine and N,N-dimethyl-l ,3-propanediamine.

The chain extension reaction may be carried out at room temperature, buta temperature around 10 C in the earlier stage of reaction, where thesolution viscosity is low, is preferable, and a temperature around C isdesirable during the latter stages of polymerization, when thechain-extending reaction is completed.

Polyurethane solutions obtained by this invention have less tendency torise in viscosity with time, or togel, are more transparent, have betterspinnability, and show less tendency to phase separation between thesolvent and the polymer.

in this invention can be produced by reacting at least one kind ofglycol, polyether glycol, polyester glycol,

polyester-ether glycol, or polyacetal glycol, having a molecular weightin the range of approximately 300 to 8,000, preferably 800 to 3,000 withat least one kind or organic diisocyanate in an excess amount,preferably 150 to 200 mol percent of the amount of glycol used.

Such polyether glycols should preferably have melting points below 60 Cand second order transition points below normal room temperature.Examples are polyoxyethylene glycol, polyoxypropylene glycol,polyoxypropylene-ethylene glycol, polyoxytetramethylene glycol,polyoxypentamethylene glycol,

-polyoxyhexamethylene glycol, etc. Such polyester glycols shouldpreferably be those obtained by polycondensation of an aliphaticdicarboxylic acid or aromatic dicarboxylic acid with an aliphatic glycolor a polyester blycol, such as polycaprolactone, obtained byring-opening polymerization of a lactone. Useful aliphatic dicarboxylicacids include succinic acid, adipic acid, pimelic acid, suberic acid andsebacic acid, and useful aromatic dicarboxylic acids includeterephthalic acid and hexahydroterephthalic acid. Such useful aliphaticglycols include ethylene glycol, propylene glycol, butylene glycol,hexamethylene glycol, decamethylene glycol and neopentyl glycol.

Organic diisocyanates suitable for producing the urethane prepolymer foruse in this invention include l,6-hexamethylenediisocyanate,cyclohexylenediisocyanate, paraphenylenediisocyanate, naphthylene-l,5-diisocyanate, toluylene methane 4,4-diisocyanate,azobenzene-4,4-diisocyanate l-isopropylbenzene-3 ,5 -diisocyanate,dicyclohexylmethylene-4,4-diisocyanate, etc., among whichdiphenylmethane-4,4'-diisocyanate is especially suitable. Organicdiisothiocyanates corresponding to the above may also be used.

The polar solvents useful in the method of this invention includedimethylformamide, dimethylacetamide, dimethylsulfoxide andhexamethylphosphoramide.

diisocyanates, diphenyl- Furthermore, by applying the method of thisinvention, the abnormal climbing of solution up the agitator shaft thatwe often see in the course of chain-extension by other methods is seldomwitnessed. It is also an advantage of this method that the amount ofchain terminator needed in this method is smaller than in the otherhitherto known methods. Moreover, we can produce, by this method, stableurethane solutions of higher concentrations and viscosities.

Polyurethane solutions obtained by the method of this invention have amolecular weight distribution in a narrow range, and are homogeneous.

. Polyurethane solutions obtained by this invention can be madev intoshaped elastorners by the usual methods. For instance, polyurethaneelastic filaments made from these solutions by the usual dry-spinningmethods are as good in mechanical properties as those formed fromsolutions conventionally made. Furthermore, spinning of these solutions30 days after their preparation produced filaments no different fromones spun immediately after the solution was made. In contrast,conventionally made solutions all gelled within a week. Solutionsproduced by this invention also have the advantage of prolonging thefilter and spinnerette life as well as minimizing yarn breaks occurringimmediately after extrusion from the nozzle, in contrast to solutionsmade according to previously known methods.

In the following examples the methods of Nos. 1-3, 7, 8 and 12-14 arewithin the limits of Set I of the equationsand the remaining examplesare outside of those limits.

All amounts indicated by parts or percent are based on weight unlessotherwise specified.

EXAMPLE 1 A. Prepolymer:

601.8 parts of a hydroxyl-terminated 2,030 molecular weight copolyesterglycol comprising the reaction product of a 9 to 1 molar mixture ofethylene-and propylene-glycol with adipic acid was mixed with 148.2parts of diphenylmethane-4,4'-diisocyanate at 60 C. The temperature wasraised to 90 C in 30 minutes and the mixture was reacted under a drynitrogen blanket at 90 C for 60 minutes with constant agitation to forman isocyanate-terminated urethane prepolymer. The prepolymer was thendiluted with 250 parts of dimethylformamide (DMF) to reduce itsviscosity and to facilitate subsequent mixing and transfer operations.The isocyanate content of the solution was 2.365 percent.

B. Chain Extension:

1. An amine solution for chain extension use was prepared by mixingtogether 3.50 grams of methylimino-bis-propylamine, 11.59 grams ofethylene diamine and 0.46 grams of diethanolamine (chain terminator) anddiluting the mixture with DMF to a total volume of 100cc.

2. The chain extension was carried out under a nitrogen blanket at atemperature of 10 to 30 C starting with a mixture of 2,106 grams of DMFand cc of the above amine solution. To this mixture there was addedsimultaneously with vigorous stirring 2.0cc/rnin. of the amino solutionprepared in Part 8.1. and 15.6 grams/min. of the dilutedisocyanate-terminated urethane prepolymer from Part A above. Theaddition of chain extenders and prepolymer was continued for a period of47.5 minutes after which time all of the chain extenders from Part 8.1.and 95 percent of the stoichiometrically required amount of prepolymersolution had been added. At this point, the prepolymer solution additionrate was decreased to 7.8 grams/min. and continued until 97.5 percent ofthe stoichiometrically required amount of prepolymer had been added,then further decreased to 3.9 grams/min. and continued until 99.5percent of the stoichimetrically required amount of prepolymer had beenadded. The reaction was stopped at this point yielding a polyurethanesolution with a viscosity at 30 C of 400 poises, a solids content of20.1 percent and a polymer inherent viscosity of 1.25 at 30 C in DMF.Additional properties are shown in the accompanying Table I.

C. Filament Formation:

A portion of the urethane polymer solution from 8.2. was filtered andimmediately wet-spun into a 20 percent solution of DMF in water througha spinnerette having 60 holes, each hole 0.1 1mm in diameter, to producea coalesced filament bundle having a denier of approximately 420 aftersubsequent hot water extraction and hot roll drying. Other portions ofthe urethane polymer solution were wet-spun similarly after 5 days anddays storage, respectively. Solution properties as well as filamentproperties are shown in Table 1.

EXAMPLE 2 Example 1 was repeated except that chain extension was carriedout starting with a mixture of 2,106 grams of DMF and cc of the initial100 cc of amine solution. Prepolymer solution was added to this mixturewith vigorous stirring at a rate of 15.6 grams/min. whereas theremainder of the amine solution was added 10cc at a time at intervals of5 minutes. When the last 10 cc addition of amine solution was made andreacted, 80 percent of the stoichiometrically required prepolymersolution has been added. Additional prepolymer solution was added at arate of 7.8 grams/ min. until percent stoichiometry was achieved, andthen at a rate of 3.9 grams/min. until 98.9 percent stoichimetry wasreached. At this point a colorless, transparent polyurethane solution of390 poise viscosity at 30 C and 20.0 percent solids content wasobtained. The solution was spun into filaments as in Part C of Example 1above. Additional data are summarized in Table 1.

EXAMPLE 3 Example 1 was repeated except that chain extension was carriedout starting with a mixture of 2,106 grams of DMF and 25 cc of aminesolution. Prepolymer solution and amine solution were then addedsimultane- I ously with vigorous stirring at a rate of 15.6 grams/min.and 2.0cc/min., respectively, for 37.5 minutes. At this point, all ofthe amine solution and 75 percent of the stoichiometrically requiredprepolymer solution had beenadded. The remainder of the prepolymersolution was then added to 99.3 percent stoichiometry as in Examples 1and 2. The resulting urethane polymer solution had a 30 C viscosity of380 poises, a solids content of 20.1 percent, and a polymer inherentviscosity of i 1.20 in DMF at 30 C. Additional data are summarized. inTable EXAMPLE 4 prepolymer solution was then added at a rate of 3.9

grams/min. until 97.8 percent stoichiometry was reached at which pointshaft climbing occurred. The 'resulting solution had a percent solids of19.8, and was non-homogeneous, ranging in viscosity from to 420- poisesfrom one point to another. Although the solution could be spunimmediately after its preparation, it gelled within 2 days and could notbe spun further. The data are summarized in Table 1.

EXAMPLES Example 1 was repeated except that chain extension was carriedout in 2,106 grams of DMF containing 70cc of amine solution with thesimultaneous addition of 2.0cc/min. of amine solution and 15.6grams/min. of prepolymer solution for 15 minutes. At this point all ofthe amine solution had been added but only 30 percent EXAMPLE 6 Example1 was repeated except that all of the amine solution (100cc) was mixedwith 2,106 grams of DMF and then the prepolymer solution was added at arate of 15.6 grams/min. to 95 percent stoichiometry and finally at arate of 7.8 grams/min. to 97.5 percent stoichiometry at which pointshaft climbing occurred. The resulting polyurethane solution had a 30 Cviscocity of 150 poises, a solids content of 19.8 percent and gelledwithin days. Further data are summarized in Table 1.

EXAMPLE 7 A. Prepolymer:

278.6 parts of hydroxyl-terminated 1536 molecular weight copolyesterglycol comprising the reaction product of a 7 to 3 molar mixture of 1,6-hexanediol and 2,2,-dimethyl-1,3-propanediol with adipic acid, and278.6 parts of a 1,324 molecular weight polyoxytetramethylene glycolwere mixed at 50 C with 184.7 parts of diphenylmethane-4,4'-diisocyanateand 8.2 parts of 80/20 tolylene diisocyanate. The temperature was raisedto 80 C in 30 minutes and the mixture was reacted under. a dry nitrogenblanket at 80 for 60 minutes with constant agitation to form anisocyanateterminated urethane prepolymeL The prepolymer was then dilutedwith 250 parts of DMF, to yield a solution with an isocyanate content of3.136 percent.

B. Chain Extension:

1. An amine solution for chain extension use was prepared by mixingtogether 4.0 grams of Z-methylpiperazine, 14.4 grams of ethylene diamineand 0.722 grams of dibutylamine (chain terminator) and diluting themixture with dimethylacetamide (DMA) to a total volume. of 100cc.

2. The chain extension was carried out under a nitrogen blanket startingwith a mixture of 2,062 grams of dimethylacetamide and cc of the aboveamine solution at 10 C. To this mixture there was added simultaneouslywith vigorous stirring 2.0cc/min. of the amine solution prepared in partB.1. and 15.1 grams/min. of the diluted isocyanate-terminated urethaneprepolymer from Part A above. The addition of chain extenders andprepolymer was continued for a period of 45 minutes after which time allof the amine solution from Part 8.1. and 90 percent of thestoichiometrically required amount of prepolymer solution had beenadded. Further addition of prepolymer solution was continued at the rateof 15.1 grams/min. until 95 percent of the stoichiometrically requiredamount of prepolymer had been added. At this point the prepolymersolution addition rate was decreased to 7.6 grams/min. and continueduntil 97.5 percent of the stoichiometrically required amount ofprepolymer had been added, then further decreased to 3.9 grams/min. andcontinued until 99.7 percent of the stoichiometrically required amountof prepolymer had been added. The colorless, transparent polyurethanesolution thus obtained had a solids content of 20.1 percent, a 30 Cviscosity of 420 poises and a polymer inherent viscosity of 1.27measured in DMF at 30 C. The solution was spun into filaments as in PartC of Example 1 was excellent results. Additional properties are shown inTable 2.

EXAMPLE 8 Example 7 was repeated except that chain extension was carriedout starting with a mixture of 2,062 grams of dimethylacetamide (DMA)and 30cc of amine solution to which both amine and prepolymer solutionswere added simultaneously at the same rates as in Example 7 for a periodof 35 minutes. At this point all of the amine solutions and percent ofthe stoichiometrically required prepolymer solution had been added.Further prepolymer solution was added as in Example 7 until 99.1 percentstoichiometry was achieved. A colorless, transparent polyurethanesolution of 410 poises at 30 C and 20.0 percent solids content wasobtained. The solution was spun into filaments as in Part C ofExample 1. Solution and filament data are summarized in Table 2.

EXAMPLE 9 Example 7 was repeated except that chain extension was carriedout in 2,062 grams of DMA with the simultaneous addition of amine andprepolymer solutions at the same rates as in Example 7 for a period of50 minutes. At this point, all of the amine solution and 97.5 percent ofthe stoichiometrically required prepolymer solution had been added.Further prepolymer solution was then added at a rate of 3.9 grams/min.until 99.7 percent stoichiometry was reached at which pointshaft-climbing occurred. The resulting solution had a percent solidscontent of 19.7 percent and was homogeneous, ranging in viscosity fromto 525 poises from one point to another. Although the solution could bespun immediately after its preparation, it gelled within 2 days andcould not be spun further. The data are summarized in Table 2.

EXAMPLE 10 Example 7 was repeated except that chain extension wascarried out starting with a mixture of 2,062 grams of DMA and 50cc ofamine solution to which both amine and prepolymer solutions were addedsimultaneously at the same rates as in Example 7 for a period of 25minutes. At this point all of the amine solution and 50 percent of thestoichiometrically required prepolymer solution had been added as inExample 7 until 98.6 percent stoichiometry was reached at which pointexcessive shaft-climbing occurred. The resulting solution had a solidscontent of 19.9 percent and a viscosity of 380 poises at 30 C, andgelled within 10 days of its preparation. The data are summarized inTable 2.

EXAMPLE 1 1 Example 7 was repeated except that the 2.062 grams of DMAwas first mixed with all of the amine solution (100cc) and thenprepolymer solution was added at a rate of 15.1 grams/min. until 95.6percent stoichiometry was reached when shaft-climbing occurred. Theresulting polymer solution had a solids content of 19.5 percent andgelled within 5 days of its preparation. The data are summarized inTable 2.

EXAMPLE 12 A. Prepolymer:

527.4 parts "of 'a 1,516 molecular weight polyoxytetramethylene glycolwas mixed at 50 C with 168.7 parts of diphenylmethane-4,4"diisocyanateand 3.9 parts of P-xylylene diisocyanate. The temperature was raised to65 C for 60 minutes with constant agitatibn to form anisocyanate-terminated urethane prepolymer. The prepolymer was thendiluted with 300 parts of DMA to yield a solution with an isocyanatecontent of 2.774 percent.

B. Chain Extension:

1. An amine solution for chain extension use was prepared by mixingtogether 20.0 grams of 1,2- propylene diamine and 0.697 grams ofdibutylamine and diluting the mixture with DMA to a total volume of100cc.

2. Chain extension was carried out under a nitrogen blanket startingwith a mixture of 1,667 grams of DMF and 15cc of the above aminesolution at 10 C. To this mixture there was added simultaneously withvigorous stirring 1.79cc/min. of the amine solution prepared in PartB.1.'and 16.5 grams/min. of the diluted isocyanate-terminated urethaneprepolymer from Part A above. The addition of chain extender andprepolymer solutions was continued for a period of 47.5 minutes afterwhich time all of the amine solution and 95 percent of thestoichiometrically required amount of prepolymer solution had beenadded. Further addition of prepolymer solution was continued at a rateof 8.3 grams/min. until 97.5 percent stoichiometry was reached, and thencontinued at arate of 4.2 grams/min. until 99.6 percent stoichiometrywas achieved. At this point a colorless, transparent polyurethanesolution was obtained with a solids content of 22.9 percent and aviscosity of 750 poises at 30 C. The data in Table 3 indicate theexcellent stability of this solution and the properties of yarnsobtained by dry-spinning.

EXAMPLE l3 Example 12 was repeated except that during chain extensionthe rate of addition of the amine solution was increased to 2.13cc/min.The addition of amine solution was completed in 40 minutes at whichpoint the prepolymer was at 80 percent of stoichiometry. Furtherprepolymer was added as in Example 12 until 99.2 percent ofstoichiometry had been reached, yielding a polyurethane solution with asolids content of 22.9 per- Table 3 indicate the excellent solutionstability and dryspun yarn properties obtainable.

EXAMPLE 14 Example 12 was repeated except that during chain extensionthe rate of addition of the amine solution was further increased to2.62cc/min. so that the addition of amine solution was completed in 32.5minutes at which point the prepolymer was at 65 percent ofstoichiometry. Further prepolymer was added as in Example 12 until 99.1percent of stoichiometry had been reached yielding a colorless,transparent polyurethane solution with a solids content of 22.9 percentand a 15 viscosity of 720 poises. The data in Table 3 indicate theexcellent solution stability and dry-spun yarn properties obtainable.

EXAMPLE 15 Example 12 was repeated except that chain extension wascarried out in 1,667 grams of DMA containing 4009 of amine solution withthe simultaneous addition of 2.0cc/mm. of amine solution and 16.5grams/min. of

prepolymer solution for 30 minutes. At this point all of the aminesolution had been added and 60 percent of content of 22.8 percent and aviscosity of 710 poises,

but gelled within 10 days of its preparation and became unspinnable. Thesolution and yarn data are summarized in Table 3.

EXAMPLE 16 Example 12 was repeated except that all of the amine solution(100cc) was mixed with 1,667 grams of DMA and then the prepolymersolution was added at the same rates used in Example 12 until 98.0percent of stoichiometry was reached when excessive shaft climbingoccurred. The polyurethane solution obtained had a solids content of22.7 percent and an initial viscosity of 690 poises but gelled within 5days and became unspinnable. The solution and yarn data are summarizedcent and a viscosity at 30 C of 725 poises. The data in in Table 3.

TABLE 1 Time of test after solution preparation Example 1 Example 2Example 3 Example 4 Example 5 Example 6 Immediately after. 400 390 380to 420 35 150 2 days after. 450 400 390 4'20 700 5 days after... 420 420420 850 10 days after, and 446 450 470 20 days after making 460 480 510Yarn proportion:

Spun immediately after solution preparation:

Denier (d.) 427 425 Tenacity (g.-/d.) 1.137 1. Elongation (percent 602600 300% modulus (27d) 0.153 0.150 Spun 5 days after solutionpreparation:

Denier (d.) 42A 423 Tenacity (g./d.) 1.140 1.121 Elongation (percent)611 610 3% Modulus (g./d.) 0.155 0.151 Spun 10 days after solutionpreparatio Denier (d.) 420 421 Tenacity (g./d.). l 1.132 1.115Elongation (percent) 600 602 300% modulus (g./d.) 0.157 0.154

1 Gelled. Unspinnable.

TABLE 2 Time of test after solution preparation Example 7 Example 8Example 9 Example 10 Example 11 Viscosity of polymer solution (poise):

Immediately after preparation 420 410 100 to 525 380 75 2 days afterpreparation 430 425 475 850 days after preparation 442 025 days afterpreparation 450 20 days after preparation 475 Yarn proportion:

Spun immediately after solution preparation:

Denier (d.) 43D Tenacity (g./d.) 1. 217 Elongation (percent) 585 300%modulus (g./d.) 0. 226 Spun 5 days after solution preparation:

Denier (d.) 432 Tenacity (g./d.) 1.223 Elongation (percent) 590 300%modulus (g./d.) 0.224 Spun 10 days after solution preparation:

Denier (d.) 424 Tenacity (g./d.) 1.225 Elongation (percent) 591 300%modulus (g./d.) 0. 223

1 Turned white and gelled. 1 Unspinnable.

Gelled.

TABLE 3 Time of test after solution preparation Example 12 Example 13Example 14 Example 15 Example 16 Viscosity of polymer solution (poise):

Immediately after preparation 750 725 2 days after preparation 760 725 5days after preparation.. 730 735 10 days after preparation. 790 755 20days after preparation-.. 820 730 Yarn proportion:

Spun immediately alter solution preparation:

Denier (d.) 423 422 Tenaclty (g-l -l 1. 37s 1. 381 Elongation (percent).550 547 300% modulus (g./d.)-...... 0. 259 0. 266 Spun 5 days aftersolution preparation.

Denier (d.) 420 410 Tenacity (g./d. 1.382 1.374 Elongation (percent).560 549 modulus (g 0. 265 0. s Spun 10 days after sol Denier (d- 418 416Tenacity (g.ld.) 1.380 1.375 Elongation (percent). 550 551 300% modulus(g./d.) 0. 261 0. 260

1 Gelled.

2 Unspinnable.

What is claimed is: 1. In a batch process for producing a solution of asubstantially linear polyurethane formed by reaction in solution of anisocyanate-terminated prepolymer with a in which D represents the amountof diamine and P the amount of prepolymcr which have been added at anytime, during the period extending from the beginning to the completionof diamine addition, expressed as a mole percent of the respective totalamount of each to be added for completion of the reaction.

2. The improvement of claim 1 wherein:

3. The improvement of claim 1 wherein the diamine extender comprises alower alkyl diprimary diamine.

4. The improvement of claim 3 wherein said diamine is ethylene diamine.

i i i i l

2. The improvement of claim 1 wherein:
 3. The improvement of claim 1wherein the diamine extender comprises a lower alkyl diprimary diamine.4. The improvement of claim 3 wherein said diamine is ethylene diamine.